1. Field of the Invention
The present invention relates to tightly-fitting food packages and food packaging methods.
2. Description of Related Art
In the preservation of food quality, oxidative degradation by oxygen is one of factors affecting the food quality. When foods are in the presence of oxygen, lipids or pigments in the foods are oxidized to cause lipid oxidation products or pigment discoloration, greatly deteriorating the food quality.
Oxidative degradation of foods by oxygen during storage or transportation has been prevented by modified atmosphere packaging in which packages are filled with a single or a mixture of inert gases such as nitrogen, carbon dioxide and argon, or by vacuum packaging in which packages are evacuated.
Modified atmosphere packaging with carbon dioxide gas is known to inhibit the growth of microorganisms in foods during storage, by the bacteriostatic effects of carbon dioxide. In the conventional modified atmosphere packaging, however, the gas is filled in a head space in the package and consequently the package volume is larger than the volume of the food packaged therein. Thus, the transportation efficiency is lowered and the storage space is increased.
Vacuum packaging of unsterilized foods such as raw foods entails strict temperature control during storage because such foods are at risk of the growth of microorganisms during storage.
To address these problems, Patent Document 1 discloses a food packaging method which involves filling a gas containing 50-100% by volume carbon dioxide. However, the patent document does not specify the amount of the fill gas. Filling the gas in a very large amount increases the volume of gas spaces such as head spaces, and it is difficult that the packages have a minimized volume. The fill gas substantially disclosed in the patent document is a carbon dioxide/nitrogen mixture gas. However, the nitrogen gas has low solubility in water and this causes an increase in space volume.
Patent Document 2 discloses a technique in which a water-containing processed food is placed in a package while the surface temperature of the food is maintained at 70 to 140° C. and the processed food accounts for 60 to 95% by volume of the package, and the package is filled with carbon dioxide and then sealed. This technique involves packaging the food while the food is heated to the above surface temperature and thus cannot be adopted for raw foods such as meat.
Patent Document 3 discloses a method wherein a food that absorbs carbon dioxide is packaged and solid carbon dioxide such as dry ice is placed in the package. In this method, however, the contact with dry ice causes freezer burn. Further, this method does not sufficiently address deaeration of oxygen or the like, and it is likely that oxygen or the like remains in the packages.    Patent Document 1: JP-A-S60-110663    Patent Document 2: JP-A-H10-225267    Patent Document 3: JP-A-H04-87926